This invention pertains generally to aircraft control systems and more particularly to a system for maintaining an aircraft at a constant altitude.
One type of altitude holder heretofore provided for use with an auto pilot utilizes a servomotor and a potentiometer to provide a reference signal corresponding to the altitude to be held. The servomotor positions the potentiometer in accordance with the altitude of the aircraft, and when a desired altitude is reached, the motor is stopped. Thereafter, the potentiometer provides a fixed reference corresponding to the desired altitude. This system has the advantage of holding indefinitely, but it also has disadvantages such as size, weight and speed.
Electronic sample and hold circuits using capacitive storage elements have heretofore been provided for storing analog signals. Such circuits lack the ability to hold for long periods of time because leakage currents tend to discharge the capacitors, and the signals are lost.